The present invention relates to ultrasonic nondestructive monitoring of a high temperature material. The commercially available ultrasonic transducers used to introduce the ultrasonic signal into the test specimen cannot continuously withstand the high operating temperatures encountered in high temperature operation.
The prior art technique for allowing high-temperature ultrasonic testing of materials utilizes a waveguide positioned between the test specimen and the transducer. The waveguide transmits the ultrasonic signal from the transducer to the specimen and the reflected echo from the specimen back to the transducer while at the same time providing a path between the hot specimen and the transducer over which temperature decays from the hot specimen to the transducer. One example of such prior art devices is U.S. Pat. No. 3,350,923, Nov. 17, 1967, of Cross, which uses a waveguide welded to pipes in order to ultrasonically measure wall thickness at elevated temperature. Welding metallurgically alters the wall of the test specimen. This change causes noisy signal and destroys the continuity of the pipe. Cross describes a variety of weld joints between the waveguide and the test specimen wall, all designed to achieve a reflective surface at the interface which would generate an interface echo signal approximately equal in amplitude to the back wall echo signal. Cross specifies that no more than 50% of the cross-sectional area of the delay line should be fused to the pipe in order to achieve an interface echo signal amplitude equal to the back wall echo signal amplitude. Threading of the outer surface of the waveguide is used by Cross to reduce signal side wall reflections.
It is therefore an object of this invention to provide an improved device for coupling a waveguide to a test specimen.
Another object of this invention is to provide a pressure coupling for an ultrasonic waveguide to a material in high-temperature applications to avoid metallurgical altering of material.
Another object of the invention is to provide a waveguide that is temporarily connected to the test material without deforming the test material.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.